Olefins, particularly ethylene and propylene, are desirable as a feed source for making derivative products such as oligomers, e.g., higher olefins, and polymers such as polyethylene and polypropylene. Olefin feed sources have traditionally been produced by cracking petroleum feedstocks.
Oxygenate feedstocks, however, are becoming an alternative to petroleum feedstocks for making olefins, particularly large quantities of ethylene and propylene, for the production of higher olefins and plastic materials. In general, the olefins are formed by contacting the oxygenate components, such as methanol, with a molecular sieve catalyst to catalytically convert the oxygenates to olefins. These types of processes are generally referred to as oxygenate-to-olefins and methanol-to-olefins (collectively referred to herein as MTO) processes.
Many of the MTO processes are carried out using fluidized bed type reactors. Such reactors are generally operated at low pressures and elevated temperatures, using a molecular sieve type catalyst. Operating at supercritical conditions has also been suggested.
U.S. Pat. No. 4,849,575 (Lewis) discloses a process for producing olefins. In a step (a), hydrogen and at least one carbon oxide are contacted in a first reaction zone at conditions effective to chemically react the hydrogen and carbon oxide and produce at least one product, e.g., methanol, in the effluent of the first reaction zone. In a step (b), the effluent containing the product is contacted in a second reaction zone at conditions effective to chemically react the product and produce olefins in the effluent of the second reaction zone. In a step (c) an olefin-enriched product is recovered from the effluent of the second reaction zone; and in a step (d) at least one of hydrogen and at least one carbon oxide from the effluent of the second reaction zone are subjected to step (a). In certain instances, it is preferred that the step (b) contacting conditions be such that the contacting temperature exceed the critical temperature of the first reaction zone effluent product or products, e.g., methanol. In other words, in certain embodiments, such product or products are preferably in the supercritical state at the step (b) contacting conditions.
U.S. Pat. No. 4,973,792 (Lewis et al.) discloses a process for catalytically converting a feedstock into a product. In a step (a) the feedstock is contacted with a fluidized mass of solid particles comprising crystalline microporous three dimensional solid catalyst in a reaction zone at conditions effective to convert the feedstock into the product. In a step (b) the particles in the reaction zone are contacted with a first purge medium to reduce the amount of at least one of the feedstock and the product in contact with the particles. In a step (c) the particles in the reaction zone are contacted with regeneration medium at conditions effective to improve at least one catalytic property of the catalyst, provided that steps (a), (b) and (c) are repeated periodically. In certain instances, it is preferred that the feedstock/catalyst contacting conditions be such that the contacting temperature exceed the critical temperature of the feedstock. In other words, in certain embodiments, the feedstock is preferably in the supercritical state at the step (a) feedstock/catalyst contacting conditions.
U.S. Pat. No. 6,046,373 (Sun) discloses a method for preparing a catalyst and the use of such catalyst for converting an oxygenate feed to olefins. The catalyst is modified or treated with the aid of electromagnetic energy. The process may be carried out in a liquid, supercritical fluid, a mixed vapor/liquid, or a mixed vapor/supercritical fluid phase.
It would be beneficial to improve the various methods of converting oxygenates to olefins. Methods that result in increase of throughput, reduction in reactor size, increase in efficiency, increase in product in specificity and increase in product production would be particularly desirable.